Question: $ B = \left[\begin{array}{rrr}2 & 0 & 1 \\ 1 & 1 & 2 \\ 1 & 2 & 0\end{array}\right]$ What is $ B^{-1}$ ?
$ = \left[\begin{array}{rrr}\frac{4}{7} & -\frac{2}{7} & \frac{1}{7} \\ -\frac{2}{7} & \frac{1}{7} & \frac{3}{7} \\ -\frac{1}{7} & \frac{4}{7} & -\frac{2}{7}\end{array}\right]$